Unionised workers may be able to negotiate with management for higher wages during periods of economic prosperity. Suppose that workers at automobile assembly plants successfully negotiate a significant increase in their wage package. How would the new wage contract be likely to affect the market supply of new cars?
Supply will shift to the left.
If the cost of resources used to produce a good increases, which will be because of increase in wages in this case, sellers will be less inclined to supply the same quantity at a given price, and the supply curve will shift to the left.